section {
    width: 400px;
    height: 400px;
    border: solid 1px black;
    position: absolute;
    left: 50%;
    top: 50%;
    margin-left: -200px;
    margin-top: -200px;
    div {
        width: 100px;
        height: 100px;
        position: absolute;
        background-color: #ddd;
        border: solid 1px black;
        &:first-child {
            left: 50%;
            top: 50%;
            margin-left: -100px;
            margin-top: -100px;
        }
        &:nth-child(2){
            left: 50%;
            top: 50%;
            margin-top: -100px;
        }
        &:nth-child(3){
            left: 50%;
            top: 50%;
            margin-left: -100px;
        }
        &:last-child {
            left: 50%;
            top: 50%;
        }
    }
}
